Age-hardening behavior, microstructural evolution and grain growth kinetics of isothermal ω phase of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-11, Vol.529, p.326-334
• Main Authors: Xu, Y.F., Yi, D.Q., Liu, H.Q., Wang, B., Yang, F.L.
• Format: Article
• Language: English
• Subjects: Age hardening; Dissolution; Evolution; Grain growth; Grain growth kinetics; Martensite; Microstructural evolution; Microstructure; Surgical implants; Titanium base alloys; ω Phase
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.09.035

► α″ Martensite decomposed by the mode of α″ → α″ + β → β + ω → α + β during aging. ► ω Competed to grow with α first, and then transformed to α after longer aging time. ► Dense ω and α precipitates distributing in β matrix resulted in the peak hardness. ► The grain-growth exponent, n for ω iso, was computed to be in the range of 0.23–0.26. ► The activation energy for ω iso grain growth, Q g was calculated to be 119.7 kJ/mol. Age-hardening behavior, microstructural evolution and the grain growth kinetics of isothermal ω during aging treatments of Ti–25Nb–10Ta–1Zr–0.2Fe alloy were investigated. The results showed that in addition to martensite α″, a small amount of α and athermal ω was observed in the β matrix after solution treatment. The decomposition of martensite α″ and the transformation from athermal ω (ω ath) to isothermal ω (ω iso) occurred at the early stage of aging. ω iso firstly competed to grow with α phase, and then dissolved and transformed into α phase. The growth and dissolution of ω iso was accelerated with increasing aging temperature. Finally, the α + β stable microstructure was obtained after aging for 280, 200, 24 and 2 h at 623, 673, 743 and 773 K, respectively. The alloy showed stronger age-hardening response at intermediate temperatures of 673 and 743 K, while exhibited weaker age-hardening response at lower temperature of 623 K and higher temperature of 773 K. The uniform distribution of dense ω iso and α precipitates in the β matrix with moderate size resulted in the peak micro-hardness values. The grain growth of ω iso obeys an asymptotic law, and the grain-growth exponent, n, was computed to be in the range of 0.23–0.26 at temperatures in the range of 623–743 K. The activation energy for ω iso grain growth, Q g was calculated to be 119.7 kJ/mol.